The present invention concerns nozzles for spraying liquids, which can be used in the most diverse applications, for example spray pumps, evaporators, combustion burner nozzles, internal combustion engine injectors.
The invention applies more particularly to spray nozzles in which the liquid to be sprayed is fed into a central swirl chamber via lateral fluid inlet passages injecting the liquid tangentially, the liquid then leaving the central swirl chamber in an axial outlet direction through a coaxial outlet passage.
Document FR 2 324 986 describes a prior art spray nozzle. In this nozzle, the swirl chamber is conical, and the liquid is injected tangentially along the conical peripheral wall of the chamber in a forwardly oriented oblique direction. The outlet orifice has a rounded lip. A blind posterior coaxial recess is provided in the posterior wall of the swirl chamber, with a diameter less than that of the outlet orifice, to stabilize the spray cone at the exit from the nozzle.
Spray nozzles of the above kind with a central swirl chamber generally spray liquids well.
A problem which has been encountered, when using the above prior art nozzles is that, at the end of a spraying step, when the feed to the nozzle is interrupted, there is a residual outflow of fluid from the nozzle, in the form of one or more large droplets, which have not been sprayed.
In combustion applications, this leads to an increase in the level of carbon monoxide and in the level of hydrocarbons in the exhaust gases, and to soiling of the heat exchange walls, which reduces the transmission of heat and affects the efficiency of the installation.
One prior art solution consists in providing a valve at the inlet of the spray nozzle. This solution is costly, however, causes blocking and interferes with operation by introducing a threshold effect on starting. A valve of this kind also makes it essential to provide sufficient fluid pressures on the upstream side for it to operate correctly, which are significantly greater than the pressure needed for the nozzle itself to operate.
The problem addressed by the present invention is that of designing static, low-cost means of inhibiting outflow from the spray nozzle when its feed is interrupted.
The invention results from the surprising observation that, during operation of a spray nozzle with a central swirl chamber, if a swirl of liquid is formed in the swirl chamber in a plane generally perpendicular to the axis of the outlet orifice and if a posterior coaxial opening of sufficiently large diameter is provided, residual outflow from the nozzle is inhibited as soon as the feed of liquid to the nozzle is interrupted.
To this end, the invention provides a spray nozzle having:
a central swirl chamber delimited by a peripheral wall with a shape of revolution about a longitudinal axis, an anterior wall incorporating a coaxial outlet passage, and a posterior wall,
at least one lateral fluid inlet channel in the peripheral wall, opening into the central swirl chamber and shaped to inject the fluid tangentially into the swirl chamber,
a posterior coaxial opening provided in the posterior wall of the swirl chamber.
Furthermore:
the lateral fluid inlet passage(s) are shaped to inject the fluid into the swirl chamber in a direction substantially perpendicular to the longitudinal axis,
the size and shape of the posterior coaxial opening inhibit any residual outflow of fluid via the coaxial outlet passage as soon as the fluid feed to the inlet of the spray nozzle is interrupted.
The posterior coaxial opening is preferably a shape of revolution about said longitudinal axis.
It has been found that good results for inhibiting residual outflow of liquid are obtained by providing a posterior coaxial opening having a diameter greater than the diameter of the coaxial outlet passage, more advantageously in the range from 1.2 times to twice the diameter of the coaxial outlet passage.
In practice, the width of the posterior coaxial opening can be in the range from the length of the coaxial outlet passage to five times that length.
Lengths which are too short do not inhibit residual outflow. Lengths which are too long do not have any apparent additional effect.